1. Field of the Invention
The present invention relates to a resist film forming method and a resist coating apparatus for forming a resist film on the front face of a substrate such as a semiconductor wafer, a liquid crystal display device (LCD) substrate or the like.
2. Description of the Related Art
In a process of photolithography in the fabricating process of a semiconductor device, for example, a resist coating processing for forming a resist film on the front face of a semiconductor wafer, and after an exposure processing of a pattern to the semiconductor wafer coated with a resist, a developing processing for developing the pattern, are performed. In the resist coating processing, a spin coating method or the like is often employed as a method for coating with a resist solution on the front face of the semiconductor wafer uniformly.
FIG. 12 shows an appearance of a conventional coating processing unit using the above spin coating method. For instance, in a state where a semiconductor wafer W is securely held by vacuum adherence by means of a spin chuck 141, the semiconductor wafer W is rotated with the spin chuck 141 by means of a rotary drive means (not shown), and a resist solution is dripped onto almost the center of the front face of the wafer W from a resist nozzle 142 disposed above the semiconductor wafer W. The dipped resist solution is spread out in the direction of the radius of the wafer W by centrifugal force. Thereafter the dripping of the resist solution is stopped, and the semiconductor wafer is rotated at a predetermined speed to thereby draining the excess resist and drying the semiconductor wafer W. As a result, a resist film with a predetermined thickness is formed on the semiconductor wafer.
Moreover, in processes after the resist solution coating process, the semiconductor wafer coated with the resist solution is subjected to prebaking processing and cooling processing. Thereafter the semiconductor wafer is subjected to exposure processing by means of an aligner, and then post-exposure baking processing and cooling processing, thereafter developing processing to form a circuit pattern with a predetermined line width, and then post-bake processing is performed.
When the relation between the film thickness of the resist film on the semiconductor wafer and the line width of the circuit pattern which is formed on the semiconductor wafer in such a manner that the resist film is exposed into a predetermined pattern and thereafter developed is graphed, a predetermined curved line is obtained. Therefore, when the line width of the circuit pattern is designated, the film thickness of the resist film can be determined in correspondence with the line width of the circuit pattern from the curved line.
The circuit pattern needs to be formed with quite high accuracy. However, since the film thickness of the resist film somewhat varies, there occurs a case where variations in line width corresponding to changes in it resist film does not satisfy the required accuracy depending on the designated film thickness of the resist film. Accordingly, it is required that a line width has less variations corresponding to the changes in resist film thickness and that a line width with required accuracy can be obtained even within a normal range of the resist film variations.
An object of the present invention is to provide a resist film forming method and a resist coating apparatus in which the line width of a circuit pattern after development is not likely to vary regardless of changes in film thickness of the resist film formed on a substrate.
To solve the above problem, according to the first aspect of the present invention, in a resist film forming method for forming a resist film by supplying a resist solution onto the front face of a substrate housed in a processing case, a relation between the film thickness of a resist film and the line width of a circuit pattern when the resist film is exposed into a predetermined pattern and thereafter developed is obtained in advance, from that relation, a line width with less variations corresponding to the changes in resist film thickness is selected from among line widths within a designated region to form a resist film to have the film thickness corresponding to the selected line width.
In this case, the relation between the resist film thickness and the line width of the circuit pattern is a relation that the line width of the circuit pattern varies in a wave form corresponding to the resist film thickness, from that relation, a line width of an approximately maximum value or an approximately minimum value is selected from among line widths within a designated region and the resist film can be formed to have the film thickness corresponding to the selected line width.
According to the second aspect of the present invention, a resist coating apparatus for forming a resist film by supplying a resist solution to the front face of a substrate housed in a processing case comprises: rotation means for rotating the substrate at a variable speed; a resist solution supply nozzle for supplying the resist solution to the substrate; and a control mechanism for controlling a rotation condition of the rotation means and the supply amount of the resist solution supply nozzle, in which a relation between the film thickness of the resist film and the line width of a circuit pattern when the resist film is exposed into a predetermined pattern and thereafter developed is set, from that relation, a line width with less variations corresponding to the changes in resist film thickness is selected from among line widths within a designated region, so that the resist film is formed to have the film thickness corresponding to the selected line width.
According to the present invention, the relation between the film thickness of the resist film and the line width of the circuit pattern when the resist film is exposed into a predetermined pattern and thereafter developed is obtained in advance, from that relation, a line width with less variations corresponding to the changes in resist film thickness is selected from among line widths within a designated region to form the resist film to have the film thickness corresponding to the selected line width. Therefore, the line width of the circuit pattern after development can be made to resist variation regardless of changes in film thickness of the resist film formed on the substrate. Specifically, since the relation between the film thickness of the resist film and the line width of the circuit pattern is a relation that the line width of the circuit pattern varies in a wave form corresponding to the resist film thickness, from that relation, a line width of an approximately maximum value or an approximately minimum value is selected from among line widths within a designated region and the resist film is formed to have the film thickness corresponding to the selected line width, thereby variations in line width of the circuit pattern corresponding to the changes in resist film thickness can be made quite small.
These objects and still other objects and advantages of the present invention will become apparent upon reading the following specification when taken in conjunction with the accompanying drawings.